Topic: Stroker build- '76 cb750k6

[EnginebyAdam]

Hey guys great site. I build performance engines for a living and have been working on the dohc 750's for a while but I have no experience with the sohc's. That has never stopped me all the same

I have been digging through the posts here and have come across a lot of different approaches on the stroker builds. I am not looking to go max effort, but I need some impressive times on the strip. This is a drag only bike, we plan on a slick, wheelie bars as well as a custom frame.

I am still gathering information on all this but as of now I have the cb900 crank, cb900 rods (shot peened) with cb1100f rod bolts. I also have the cb900 sleeves. I have had Cometic make me a footer before so I'll go with them again for that part unless things change. I have a GL1000 in mind to donate the drive gear.

I have found a few posts by jweeks on this subject but where I am not familiar with the process I was hoping you guys might have a few book marks you could pass along.

I will be breaking down the '76 shortly so once I get in there I'll be able to see what needs to be done with the chain tensioners, primary and cam. Chances are I'll have lots of questions after I get in there.

On another note my buddy offered me a F top end so I'll have to size up which head to use once I get into this.

Well that's all I got right now, basically research mode. One of the guys over on the cb1100F site used to drag race these and the dohc's I'll have to get in touch see if he can have a chat.

[turboguzzi]

check memeber's mec mega thread on a stroker

[EnginebyAdam]

check memeber's mec mega thread on a stroker

I'll look into it now. Thanks.

[jaguar]

In to see how this turns out.

[dragracer]

Welcome to the forum Adam. Looking forward to your build. Check in with Jon Weeks and Bear. The thread by Bill Benton on   "a bike is born" has tips from both of the guys I mentioned and is specifically about the 900F striker build using off the shelf parts. Pistons, crank, rods and cam chain.

[jweeks]

     Remember that the crank ends are opposite for the DOHC 900 crank from the SOHC 750 one. You have to machine away the taper end of the 900F crank to match the points recessed end like the 750 one. The metal is relatively soft and machineable. You have to use the 900F seals in the 750 cases to prevent oil leaks. You have a splined end with a threaded hole in the center of the crank at the other end. That's what you use to attach a nut for external starters or some form of kick starter gear/one way clutch from a 750 on that end of the crank. It will be a total loss ignition system. HyVo primary chain from the crank will need early Goldwing parts to connect to your transmission. Tensioners for the primary chain can come from many various places. Using the stock 900F tensioner with a custom mount has been done by several forum members. Bear is a good source of information on this stuff.
     The 900F cranks still clear your cases in most places. Some clearancing of the crank throws to case webbing will be needed. It's a minor amount of filing/grinding. The 900F cranks can be lightened a fair amount. They can also be welded up and stroked another 2-3mm, depending on rods used and case clearances. You will find that your cylinder head will be the limiting factor as the displacement goes up. You've got to get the air through the motor to make power. Without significant increasing intake port size, valve sizes, carb sizes, etc., you'll limit the motor's power. I've got an 1180cc Hondamatic that I drag race that needs more head work, not more stroke. I've moved the powerband down with the stroker crank, but haven't got a normal power curve on the chassis dyno. It's limited by the cylinder head passing more air through. Cycle X has done the best job of reworking a 750 head to handle the big cc displacements available that I've seen. Speed costs, how quick do you want to go? Stock crank 750's can go 10's easily. Add a stroker and 9's can be had. Get a good reworked head like Cycle X has, and high 8's might be possible.
     If you're looking to bracket race it, the Hondamatics will be much more repeatable than their clutch equivalent. Tell us what you're looking to do...

                                                     Jon Weeks

[Bill/BentON Racing]

Welcome,you've come to the right place! Yes Bear,Jon Weeks,,Mec, and others have experience in what you are building. There's another member here who probably could be a big help......if you want more CFM! The CB750F77-78 over here,is the best head if available. Bigger valves,better ports,combustion chamber,etc.Head is stamped"410"
on upper backside.Kenny has the best Ive seen....,but was a very highly modified stock head.  Intake ports relocated straight shot,38 mm intakes,34 mm ex valves. See fellow member Mike Rieck for your porting needs,he's in touch with Kenny weekly. We are all meeting in Bradenton in Nov. for the World Finals.Nov. 8-10th. Come join us,Bill

[EnginebyAdam]

Wow guys thanks for the responses I will dig into the thread mentioned promptly. I have a 77-78 F head from a buddy for pennies I will confirm it is the one mentioned.

I am defiantly looking for an off the shelf build if at all possible, trying to use what I have in my garage I have this piece that I hope to use from the Captain over on the 1100F site that I bought for my 985cc dohc build if it can work. Will have to see when I get there, not sure on the internals of these yet so I'll take it as it comes.

[EnginebyAdam]

Well it's nice to be digging into research mode again, and there is lots to read here. I have read mec's thread as well as "stroker cranks and big motors...", "a bike is born..." completely.

I can honestly say I have a lot of the parts on hand, I also have the guide and tensioner for the primary chain. In the dohc realm we like to use the 1100F set up, tensioner and guide, because it is wider and supports the primary chain more, but the 900 setup seems to be more common here. I also just ordered the GL 1000 primary for the conversion.

I guess my first major question is what piston should I use? I am limited by the 15mm pin for the 900 rods. I also know these engines can run higher CR's than the DOHC's as well but where is a good range for a dependable low 10's bike? I have seen threads for the gpz750 pistons which looked good but they are 66mm I think stock and the domes are very large. Also the RC 45 pistons but they are 17mm wrist pins. I am looking for the max piston size of 67.5mm which would give me the 1000cc. The cb900 liners I plan to use only like up to that bore size anyway, or so it seems with the dohc's.

I am also having a hard time finding info on the kicker set up, or external starter for the cb900 crank set up.

The plan is to spend the major money on the cams/head, transmission and clutch as well as any oiling mods that need to be done. All this is besides the drag frame, slick and bars.

Cheers, Adam

[dragracer]

Bill Benton's thread outlines the type of off the shelf pistons recommended in his build. If i remember correctly they are stock Honda forged pistons with the correct pin diameter- take a thorough read on his thread.

[EnginebyAdam]

Bill Benton's thread outlines the type of off the shelf pistons recommended in his build. If i remember correctly they are stock Honda forged pistons with the correct pin diameter- take a thorough read on his thread.

Looks like he used VRF 750 pistons but they have the 17mm pins. I would jump on a set of 1100F rods to use the 17mm pistons but they are like hens teeth even on the 1100F site.

[Jerry Rxman Griffin aka MuthaF'er]

Aren't the CycleX 915 pistons 67.5mm?

[jweeks]

Rick Stetson recommended to me to keep it at 12:1 max if you are planning to drive your bike back to the pits after your quarter mile pass. If you tow back, the sky's the limit or at least the octane rating of your fuel.

                                                            Jon Weeks

[Bill/BentON Racing]

Well,I got my answer.....still need a set of 1100F rods!  915cc Kenny's kit Wiseco pistons weigh 155 grams.Jay has 1000 cc kits,J&E will make what you want.Lots of 15 mm kits. Good Luck and find "us" some rods!  Bill
I'm using XL 250 will post a pic tomorrow. Bear very big help,he's sent me in the rt direction more than once.Jon also.Kenny,Mike,Jay, all willing to help.Alongvwith most anyone on this awesome forum!

[jweeks]

Wouldn't a 915 kit with a +6mm stroke get you around a 1,000cc motor? Yes, the 900F cranks were out in the early 80's. Lockup clutch, as much compression as the pistons will allow, a good top end cam, a well ported head, undercut transmission,  and you're on your way to a mid/low 10 second bike.

                                                                   Jon W.

[dragracer]

I wish i could find a multi stage lockup for mine.

[EnginebyAdam]

I read in Bill's thread he was having a bit of trouble after he started running a lock up clutch. I am going to dig into transmission mods next.

With all the extra pounding of a clutch drag bike versus the auto bike's I'm wondering if the cb900 rods will hold up even shot peened and good bolts. Although I have read good things with the midget racers. Went thru the options for pistons and there are lots. Would like to go 68mm to give me the 1002cc if I can. I'd like to shoot for 12:1 maybe 11.5:1 depending on the head.

The stock cb900 pistons weight 230.3g on average with rings, clips and pins. Plan on using the cb900 rods if I can, they weight 390g's. From what I got off cycle x's site there pistons are 155g's and four grams lighter than stock. That is over the 50g rule unless that is just piston weight not dressed which would be a bit better. I have to look at balancing I saw that Mec sent his out for balancing. I hope a buddy of mine can help me out here to get this part right.

I still have to look into the kicker/starter setup. If I plan on running 11.5:1 - 12:1 I'll want the starter for sure.

[Medyo Bastos]

i may be willing to part with a set of 67mm arias pistons with new rings from total seal, new wrist pins, decked jugs with new sleeves, freshly bored and honed, just waiting for a motor to drop into...  head is polished, opened up to 67mm, ported, cc'd, new guides, springs, anodized retainers, etc... (11:5:1)

[evan77]

i may be willing to part with a set of 67mm arias pistons with new rings from total seal, new wrist pins, decked jugs with new sleeves, freshly bored and honed, just waiting for a motor to drop into...  head is polished, opened up to 67mm, ported, cc'd, new guides, springs, anodized retainers, etc... (11:5:1)

Hi Medyo,
I might be interested in this setup. The pistons are 15mm pin I would assume? I was planning on using a spare set of CB1100F rods that I have but I suppose I could bush the small end to 15.
Let me know if you are really interested in selling.

Thanks,
Evan

[Medyo Bastos]

yes, 15mm wrist pins.

let me do some brain storming, and number crunching.  i will let you know.

[Sam Green Racing]

i may be willing to part with a set of 67mm arias pistons with new rings from total seal, new wrist pins, decked jugs with new sleeves, freshly bored and honed, just waiting for a motor to drop into...  head is polished, opened up to 67mm, ported, cc'd, new guides, springs, anodized retainers, etc... (11:5:1)

Hi Medyo,
I might be interested in this setup. The pistons are 15mm pin I would assume? I was planning on using a spare set of CB1100F rods that I have but I suppose I could bush the small end to 15.
Let me know if you are really interested in selling.  Bill here,Would trade you some MTC alum rods or RC H/D with bushings installed, shot peened, etc. Both 15mm pins.

Thanks,
Evan

[EnginebyAdam]

I found a lot of info regarding undercutting and who can do the process. I am still looking for info on either a four or three speed transmission. I found with my DOHC 810cc that I would of much preferred a properly geared four speed if it was a drag only setup for the 1/4. We do not want an automatic, thinking air shifter or electric shift. I have been going through jweeks posts all the same

Thinking I will bump up to aftermarket rods in the 1100/900 length for the better ratio. By the time you get a set of 1100 rods now you are half way to a set of aftermarkets. I'm sure the cb900 rods I have are fine but I'll save them for my DOHC 985cc as was planned.

The head my buddy has is an F head but is a '75. Will take a look at it all the same.

Looking into the ignition system now. I run a Dyna 2000 system on my DOHC 810cc find it great. Might try to go the MSD route with this one, cycle x looks good too.

Any recommendations would be great guys, thanks.

[jweeks]

My opinions:
Air shifter with CO2 bottle. Get an auto shift electronic box to shift at a given rpm. (either way, you're building an automatic) A lockup clutch to launch with less worries.
MSD MC-3 ignition (used if on a budget, MC-4 if you want to extract the most possible from the motor on the dyno) Usually the only option that you can get contingency money for using at big drag events. Yes MSD is going through bankruptcy. Product is still available.
The rod problem is that inexpensive aftermarket steel 1100F rods don't exist. Carrillo's are expensive to most build budgets.
Cylinder head is where the money should go. F heads are a good start, but check how you are going to mount the carbs to that head. Manifolds are difficult/impossible to find. A good set of 34/36 mm carbs aren't cheap purchased in the Honda spacing. Used has it's advantages for us on a budget.
Don't even look for a 3/4 speed for your SOHC Honda. Too rare/too expensive. Won't get you much of any improved performance. Quarter Jr. software can check the tranny theory you're using and give the changes in ET. That's the cheap way to find out what really works. If you think that the 3/4 speed tranny will help with lower ET's, save a lot of $$ and add nitrous. You'll run quicker for less $$ spent.

     What class/category are you trying to build for? Most all bikes at the local dragstrip level are bracket racing. Heads-up racing on an index would have your Honda at a disadvantage. (9.90/8.90 usually are the slowest two) Air cooled motors are at a handicap to the water cooled higher horsepower Suzuki/Kawi's that are out there. They would be always chasing you with more horsepower than you can build. They vary less round to round than your oil cooled motor will. It would be a challenge to start to compete at that level.

     Another question for your build theory- What bike type has one rider won the most rounds of motorcycle bracket racing in New England drag racing history? answer: my Hondamatics. I know that they're not as sexy as the clutch equivalent, but they sure do win a lot. Don't use Sam's Hondamatic build as a guide. Until you launch consistently off of the back brake, the bike is a random number generator. Sam's bike isn't there yet. My 1180 'matic runs high 10's at 124 mph in the quarter mile. Not as quick as you can build a clutch equivalent, but still respectable for a 70's Honda motor.

     Good luck with your build.

                                                        Jon Weeks

[EnginebyAdam]

My opinions:
Air shifter with CO2 bottle. Get an auto shift electronic box to shift at a given rpm. (either way, you're building an automatic) A lockup clutch to launch with less worries.
MSD MC-3 ignition (used if on a budget, MC-4 if you want to extract the most possible from the motor on the dyno) Usually the only option that you can get contingency money for using at big drag events. Yes MSD is going through bankruptcy. Product is still available.
The rod problem is that inexpensive aftermarket steel 1100F rods don't exist. Carrillo's are expensive to most build budgets.
Cylinder head is where the money should go. F heads are a good start, but check how you are going to mount the carbs to that head. Manifolds are difficult/impossible to find. A good set of 34/36 mm carbs aren't cheap purchased in the Honda spacing. Used has it's advantages for us on a budget.
Don't even look for a 3/4 speed for your SOHC Honda. Too rare/too expensive. Won't get you much of any improved performance. Quarter Jr. software can check the tranny theory you're using and give the changes in ET. That's the cheap way to find out what really works. If you think that the 3/4 speed tranny will help with lower ET's, save a lot of $$ and add nitrous. You'll run quicker for less $$ spent.

     What class/category are you trying to build for? Most all bikes at the local dragstrip level are bracket racing. Heads-up racing on an index would have your Honda at a disadvantage. (9.90/8.90 usually are the slowest two) Air cooled motors are at a handicap to the water cooled higher horsepower Suzuki/Kawi's that are out there. They would be always chasing you with more horsepower than you can build. They vary less round to round than your oil cooled motor will. It would be a challenge to start to compete at that level.

     Another question for your build theory- What bike type has one rider won the most rounds of motorcycle bracket racing in New England drag racing history? answer: my Hondamatics. I know that they're not as sexy as the clutch equivalent, but they sure do win a lot. Don't use Sam's Hondamatic build as a guide. Until you launch consistently off of the back brake, the bike is a random number generator. Sam's bike isn't there yet. My 1180 'matic runs high 10's at 124 mph in the quarter mile. Not as quick as you can build a clutch equivalent, but still respectable for a 70's Honda motor.

     Good luck with your build.

                                                        Jon Weeks

As of now motorcycle racing is not very big here so we'll be racing against all the newer factory bikes. The front runner is a 1400 ninja, slightly modified, runs 9.32@146mph. If the bike can do mid 10's on engine and lower with the squeeze if I go that way, I am happy. I am thinking I will have to go with the 73mm pistons and 11:1 CR min to get reliable 10's out of the bike. Doing this on an old Honda is way more impressive than doing those numbers on a nearly stock super bike. This will be a first of it's kind around here and that's the big thing, beating up on some crotch rockets would be good too

The head spacing on the sohc vs dohc is very similar. I plan on pulling the CR31 specials off my 810cc if they can work here. Alternate mounting techniques for non traditional carbs have been used on the 1100f site with good success if the spacing is not correct. I also have a set of 36mm CV carbs as well, that might be an option. I have looked at undercutting on the transmission so I'll go that route with a lock up clutch. I plan on building this engine so it could take nos if need be. 

I have a lot of the parts already for the engine side of things so I am thinking I can spend $5000 on this project doing most of the work my self and have a solid mid to low 10's bike with a light rider (I have to lose weight ). The frame is another thing but a friend is a Tig inspector and has offered to weld it up once we get it designed.

I like MSD and hope I can find one at a good price when I get to that point.

[EnginebyAdam]

I took a trip out to see a buddy of mine this past weekend, the same guy who gave me my '76. We have been trading parts for a while now and he has quite the collection so I try to get out as much as I can. Anyway I sold him a 1982 kz1100 spectre a while back for a parts bike and I went out to see if he still had the pistons, and he did.

They are a little grubby for high performance use but for now I'm just looking for measurements. The compression height is 25.5mm on pistons which are 72.5mm bore, they also have the 17mm wrist pin. I also measured a set of stock 750 pistons and got 24.36mm compression height. Please let me know if I am off on the 750's measurement.

The obvious issue is the dome. I read a post here about machining the outer edge of the piston to get clearance for piston to head, then fly cut and shape the dome as needed. A little old school but I believe it will work with good CR numbers as well. From what info I have gathered if I were to use these pistons and cb1100 length rods with the cb900 crank I would be looking at a 8.64mm footer. Would that be too much of a foot plate under the cylinders?

The plan may change a few times before this makes it's first pass but I have to start somewhere. Cheers.